The present invention relates to a polyolefin resin modifier and, particularly, to a modifier effective in improving the film processability, stretchability and heat resistance such as low thermal shrinkage of a crystalline polyolefin resin used in an oriented film, for example, a polypropylene-based resin, a modified polyolefin resin composition and an oriented film formed from the resin composition.
An oriented polyolefin film, particularly a biaxially oriented polyolefin film is widely used as a packaging material and the like thanks to its excellent mechanical and optical properties. To produce the film, sequential biaxial orientation using a tenter system is generally employed.
In recent years, the production equipment of biaxially oriented polyolefin films has been becoming larger in size and higher in speed. When a biaxially oriented film is to be produced from a conventional general polyolefin resin with the equipment, such problems as a rise in mechanical load to a stretching machine, a reduction in the thickness accuracy of a film and the breakage of a film by stretching have arisen. Therefore, various methods for improving stretchability have been proposed. For example, JP-A 9-324014 (the term xe2x80x9cJP- Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) proposes a technology in which an amorphous component is contained in a specific amount and an isotacticity distribution is made wide. However, there still remains room for the improvement of the obtained film to produce an oriented polyolefin film having excellent film formability at the time of high-speed film formation and excellent mechanical properties and heat resistance.
Therefore, the development of a polyolefin resin having excellent stretchability which can be produced with large-sized and high-speed oriented polyolefin film production equipment has been desired.
It is therefore an object of the present invention to provide a polyolefin resin composition which has a wide temperature control range for film formation at the time of stretching and a small mechanical load, is excellent in the thickness accuracy of the formed film and stretchability, can be produced stably without being broken by stretching or the like, and is suitable for the production of a uniaxially or biaxially oriented film having excellent heat resistance such as the thermal shrinkage of the formed film.
It is another object of the present invention to provide a polyolefin resin which can provide the above excellent characteristic properties to a polyolefin resin composition obtained by mixing a crystalline polyolefin resin and a modifier comprising the same.
It is still another object of the present invention to provide an oriented film formed from the above polyolefin resin composition of the present invention.
The other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a crystalline polyolefin resin composition comprising:
(A1) 4 to 20 wt % of a polyolefin resin component having an elution temperature of 36 to 104xc2x0 C. and a molecular weight of 100,000 to 1,000,000 measured by a direct coupling method (TREF/SEC) of size exclusion chromatography (SEC) to temperature rising elution fractionation (TREF); and
(B) 96 to 80 wt % of a crystalline polyolefin resin component different from the above component (A1), the wt % being based on the total of the components (A1) and the above (B).
According to the present invention, secondly, the above objects and advantages of the present invention are attained by an oriented film formed from the above crystalline polyolefin resin composition of the present invention.
According to the present invention, thirdly, the above objects and advantages of the present invention are attained by a modifier for a crystalline polyolefin resin comprising more than 20 wt % to 100 wt % of a component having an elution temperature of 36 to 104xc2x0 C. and a molecular weight of 100,000 to 1,000,000 measured by the direct coupling method (TREF/SEC) of size exclusion chromatography (SEC) to temperature rising elution fractionation (TREF) and by a modifier comprising the same.
According to the present invention, fourthly, the above objects and advantages of the present invention are attained by a modifier for a crystalline polyolefin resin comprising 20 to 100 wt % of a component having an elution temperature of more than 116xc2x0 C. and a molecular weight of 10,000 to 100,000 measured by the direct coupling method (TREF/SEC) of size exclusion chromatography (SEC) to temperature rising elution fractionation (TREF) and by a modifier comprising the same.
The present invention will be descried in detail hereinunder.
In the present invention, the direct coupling method (TREF/SBC) of size exclusion chromatography (SEC) to temperature rising elution fraction (TREF) is an analytical method which directly couples temperature rising elution fractionation (TREF) to size exclusion chromatography (SEC) on an on-line basis and will be simply referred to as xe2x80x9cTREF/SECxe2x80x9d hereinafter. TREF/SEC is a method of evaluating the composition distribution of a polyolefin by dissolving the polyolefin (such as a polypropylene resin) crystallized in a solution in a solvent at different temperatures and continuously measuring the molecular weight distribution and the elution (concentration) of the polyolefin at each dissolution temperature. That is, an inert carrier such as diatomaceous earth or silica beads are used as a filler, a sample solution dissolved an amount of a polyolefin in a solvent such as orthodichlorobenzene as a sample is injected into the TREF column of the filler, the temperature of the TREF column is lowered to adhere the sample to the surface of the filler, the temperature of the column is elevated stepwise to a desired level, the orthodichlorobenzene solvent is passed through the column, the polyolefin component eluted at the above temperature is continuously introduced into a high-temperature SEC column, and the elution (wt %) and molecular weight distribution of the polyolefin are measured. The composition distribution of the polyolefin can be seen from a graph (the relationship between crystallizability and molecular weight is expressed by a contour or a bird""s-eye view) drawn based on the elution temperature (xc2x0 C.) and the molecular weight distribution of the polyolefin by this operation. A projection diagram of elution temperature shows a crystallizability distribution and the crystallinity distribution of the polymer can be obtained from the relationship between elution temperature and the elution (wt %) of a polymer because the elution temperature becomes higher as the elution component is crystallized more easily.
In the above method, the cooling rate of the TREF column must be adjusted to a speed required for the crystallization of a crystalline portion contained in the polyolefin sample at a predetermined temperature and can be determined experimentally in advance. The cooling rate of the column is generally set to a range of 5xc2x0 C./min or less.
Crystalline Polyolefin Resin Composition
In the present invention, it is important that the component (A1) having an elution temperature of 36 to 104xc2x0 C. and a molecular weight of 100,000 to 1,000,000 measured by TREF/SEC should be contained in the crystalline polyolefin resin composition in an amount of 4 to 20 wt %, preferably 5 to 18 wt %, more preferably 6 to 15 wt %. When the amount of the above effective component (A1) contained in the crystalline polyolefin resin composition is smaller than 4 wt %, stretchability at the time of film formation lowers, the range of film processable temperature narrows and a mechanical load rises, thereby increasing the breakage of a film by stretching and deteriorating the thickness accuracy of a film. When the amount of the above effective component (A1) is larger than 20 wt %, the thermal shrinkage of an oriented film increases with the result of a reduction in heat resistance.
Preferably, the above effective component (A1) has an elution temperature of 40 to 88xc2x0 C. and a molecular weight of the elution component at a temperature range of 44 to 68xc2x0 C. of 100,000 to 1,000,000 measured by TREF/SEC.
The crystalline polyolefin resin composition of the present invention is produced by the following methods: one in which a polyolefin containing the effective component (A1) in an amount of 20 to 100 wt % (to be referred to as xe2x80x9cthe modifier (A1)xe2x80x9d herein after) is produced and mixed with a crystalline polyolefin resin mechanically and one in which a catalyst used for the polymerization of a crystalline polyolefin resin is suitably selected and the crystalline polyolefin resin and the effective component are produced in a polymerization system and obtained as a mixture. That is, to obtain the polyolefin resin composition of the present invention with ease, the former method is preferred but the latter method is effective in many cases to obtain a uniform mixture of the modifier of the present invention and a crystalline polyolefin resin.
In the description of the present invention, a substantially uniformly united product of the effective component (A1) and the crystalline polyolefin resin is referred to as xe2x80x9cpolyolefin resin composition of the present inventionxe2x80x9d irrespective of the method of mixing the modifier (A1) and the crystalline polyolefin resin component.
The polyolefin resin composition of the present invention has a melt flow rate (MFR) of preferably 0.1 to 20 g/10 min, more preferably 1 to 10 g/10 min in consideration of its moldability into a film. The weight average molecular weight (Mw) of the polyolefin resin composition is preferably 200,000 to 800,000, more preferably 250,000 to 450,000. The molecular weight distribution expressed by the Mw/Mn ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) is preferably in the range of 2 to 20, more preferably 4 to 10 in consideration of film processing ease and the improvement of workability caused by an increase in melt tension. The above molecular weight distribution is obtained from weight average and number average molecular weights calculated from the universal calibration curve of polypropylene measured by SEC at 145xc2x0 C. using orthodichlorobenzene as a solvent from an elution profile measured under the same measurement conditions. The melting point of the polyolefin resin is preferably 130xc2x0 C. or more, more preferably 135 to 170xc2x0 C., particularly preferably 140 to 160xc2x0 C. The expression xe2x80x9cmelting pointxe2x80x9d as used herein denotes the peak temperature of a crystal melting curve at the time of temperature elevation measured with a differential scanning calorimeter (to be simply abbreviated as DSC hereinafter).
The peak temperature of an elution curve measured by the TREF of the above polyolefin resin composition is preferably in the range of 100 to 130xc2x0 C., more preferably 110 to 125xc2x0 C., particularly preferably 115 to 120xc2x0 C. in consideration of the rigidity and heat resistance of an oriented film obtained from the polyolefin resin composition. TREF is a method of evaluating the crystallizabillity distribution of a polyolefin by dissolving the polyolefin (such as a polypropylene resin) crystallized in a solution in a solvent at different temperatures and continuously measuring the elution (concentration) of the polyolefin at each dissolution temperature. That is, a sample solution having a certain concentration prepared by dissolving a sample polyolefin in an orthodichlorobenzene solvent is injected into the TREF column of an inert carrier such as diatomaceous earth or silica beads as a filler, the temperature of the TREF column is lowered to adhere the sample to the surface of the filler, the column temperature is elevated to a desired temperature linearly, the orthodichlorobenzene solvent is passed through the column, and the elution (wt %) of the polyolefin component eluted at the above temperature is measured. The crystallizabillity distribution of the polyolefin at the elution temperature can be seen by this operation. In this method, the descending speed of the temperature of the TREF column must be adjusted to a speed required for the crystallization of a crystalline portion contained in the sample polyolefin at a predetermined temperature. The cooling rate of the TREF column can be determined experimentally in advance. The cooling rate of the column is generally set to a range of 5xc2x0 C./min or less.
The amount of the component having an elution temperature of 0xc2x0 C. or less measured by TREF/SEC of the above polyolefin resin composition is preferably 10 wt % or less, more preferably 7 wt % or less, particularly preferably 5 wt % or less in consideration of the surface properties such as anti-blocking properties, scratch resistance and slipperiness of the formed polyolefin film.
Further, the molecular weight of the elution component measured at 0xc2x0 C. by TREF/SEC of the above polyolefin resin composition is preferably 10,000 to 400,000, more preferably 150,000 to 300,000 in terms of molecular weight at the peak top of a molecular weight distribution curve of the elution component at 0xc2x0 C. measured by SEC in consideration of bleed-out to the surface of a film and the formation of a fish-eye.
When the polyolefin resin composition of the present invention contains a component having an elution temperature of 36 to 104xc2x0 C. and a molecular weight of 100,000 to 1,000,000 measured by TREF/SEC in an amount of 4 to 20 wt %, it achieves excellent thickness accuracy and stretchability. The polyolefin resin composition of the present invention contains a polyolefin component having an elution temperature of more than 116xc2x0 C. and a molecular weight of 10,000 to 100,000 measured by TREF/SEC in an amount of preferably 4 to 20 wt %, more preferably 5 to 15 wt %, particularly preferably 6 to 10 wt % to further improve heat resistance such as the thermal shrinkage of the formed oriented film. The polyolefin component is the same olefin polymer or copolymer as the modifier.
Crystalline Polyolefin Resin
The crystalline polyolefin resin used in the present invention is preferably a propylene homopolymer, a propylene-xcex1-olefin copolymer containing an xcex1-olefin other than propylene as a comonomer or a mixture thereof.
The above propylene-xcex1-olefin copolymer is preferably a propylene-xcex1-olefin copolymer containing one or more xcex1-olefin monomer units other than propylene in an amount of 10 mol % or less, more preferably 5 mol % or less, or a mixture thereof. Examples of the xcex1-olefin include xcex1-olefins having 2 or 4 to 20 carbon atoms such as ethylene, butene-1, pentene-1, 3-methyl-1-butene, hexene-1, 3-methyl-1-pentene, 4-methyl-1-pentene, heptene-1, octene-1, nonene-1, decene-1, dodecene-1, tetradecene-1, hexadecene-1, octadecene-1 and eicosene-1. The above propylene-xcex1-olefin copolymer may be either an random copolymer or block copolymer. Out of these, a random copolymer is preferred.
When the above crystalline polyolefin resin is a propylene homopolymer or a propylene-xcex1-olefin copolymer which contains an xcex1-olefin other than propylene in an amount of less than 1 mol %, the fraction of isotactic pentad sequence measured by 13C-NMR indicating crystallizability is preferably 0.80 to 0.99, more preferably 0.85 to 0.98, particularly preferably 0.87 to 0.97. The fraction of isotactic pentad sequence is a fraction at which 5 propylene units determined based on the assignment of the peak of the 13C-NMR spectrum take equal configuration continuously, as reported by A. Zambelli et al in Macromolecules 13, 267, 1980.
The crystalline polyolefin resin used in the present invention is not limited to the above polypropylene-based resin and may be a polyolefin resin which is an olefin polymer or copolymer other than a polypropylene-based resin and contains a crystal portion measured by X-ray diffraction in an amount of 30% or more, preferably 40% or more.
Modifier (A1)
The modifier (A1) used in the present invention contains a component (A1) having an elution temperature of 36 to 104xc2x0 C. and a molecular weight of 100,000 to 1,000,000 measured by TREF/SEC in an amount of 20 to 100 wt % as described above. The amount of the above component is preferably 40 to 100 wt %, more preferably 50 to 100 wt %. It is more preferred that a component having an elution temperature of 40 to 88xc2x0 C. and a molecular weight of 100,000 to 1,000,000 measured by TREF/SEC should be contained in an amount of 50 to 100 wt %. It is the most preferred that a component having an elution temperature of 44 to 68xc2x0 C. and a molecular weight of 100,000 to 1,000,000 should be contained in an amount of 50 to 100 wt %.
A crystalline polyolefin resin having lower crystallinity than the above crystalline polyolefin resin may be used as the modifier (A1) without restriction. The modifier (A1) is, for example, an xcex1-olefin homopolymer, a copolymer of two or more xcex1-olefins, or a mixture thereof. The xcex1-olefin copolymer may be either a random copolymer or block copolymer. Out of these, a random copolymer is preferred. Examples of the xcex1-olefin include ethylene, propylene, butene-1, pentene-1, 3-methyl-1-butene, hexene-1, 3-methyl-1-pentene, 4-methyl-1-pentene, heptene-1, octene-1, nonene-1 and the like. Out of these modifiers (A1), a propylene homopolymer, ethylene-propylene copolymer, ethylene-1-hexene copolymer, ethylene-1-octene copolymer, propylene-1-butene copolymer, propylene-1-hexene copolymer, propylene-ethylene-1-butene copolymer and mixtures thereof are particularly preferred.
The melt flow rate of the modifier (A1) is preferably 1 to 20 g/10 min. The weight average molecular weight (Mw) of the modifier (A1) is preferably in the range of 100,000 to 400,000. Further, the molecular weight distribution (Mw/Mn) of the modifier (A1) is preferably in the range of 1.5 to 15.
Preferably, the modifier (A1) has at least one melting peak at a range of 60 to 150xc2x0 C.
The component having an elution temperature of 0xc2x0 C. or less measured by TREF/SEC of the above modifier (A1) is preferably contained in an amount of 5 wt % or less, more preferably 4 wt % or less, particularly preferably 3 wt % or less in consideration of the surface properties such as anti-blocking properties, scratch resistance and slipperiness of the formed polyolefin film.
The modifier (A1) can be prepared by polymerizing eluting components forming the modifier (A1) separately and mixing these. Alternatively, it can be prepared as a block copolymer which can attain a state in which a polypropylene component and a propylene-ethylene random copolymer component are arranged in a single molecular chain and/or a microscopically mixed state unattainable by mechanical mixing of the molecular chains of the polypropylene component and the propylene-ethylene random copolymer component. The block copolymer is preferred because it has an excellent stretchability improving effect and a more transparent oriented film is obtained.
A preferred production method for obtaining the modifier (A1) as a block copolymer comprises forming a polypropylene component (a) and a propylene-ethylene copolymer component (b) stepwise in the presence of a catalyst which comprises a metallocene compound (to be referred to as xe2x80x9ccomponent (I)xe2x80x9d hereinafter) and an aluminoxane compound or non-coordination ionized compound (to be referred to as xe2x80x9ccomponent (II)xe2x80x9d hereinafter).
The above component (I) is a known compound which is used for the polymerization of an olefin. A chiral compound represented by the following formula (1) is advantageously used as the component (I):
Q(C5H4-mR1m)(C5H4-nR2n)MX1X2 xe2x80x83xe2x80x83(1)
wherein M is the transition metal atom of the group IV of the periodic table, (C5H4-mR1m) and (C5H4-nR2n) are each a substituted cyclopentadienyl group, m and n are each an integer of 1 to 3, R1 and R2 may be the same or different and each a hydrocarbon group having 1 to 20 carbon atoms, silicon-containing hydrocarbon group or hydrocarbon group forming at least one hydrocarbon ring which may be bonded to two carbon atoms on a cyclopentadienyl ring to be substituted by a hydrocarbon, Q is a divalent hydrocarbon group, non-substituted silylene group or hydrocarbon-substituted silylene group which can crosslink (C5H4-mR1m) and (C5H4-nR2n), and X1 and X2 may be the same or different and each hydrogen, halogen or hydrocarbon group.
The component (I) is preferably a chiral metallocene compound of the above formula (1) in which M is a zirconium or hafnium atom, R1 and R2 are the same or different hydrocarbon groups having 1 to 20 carbon atoms, X1 and X2 are the same or different halogen atoms, and the hydrocarbon group Q is a hydrocarbon-substituted silylene group.
Illustrative examples of the component (I) include rac-dimethylsilylene(2,4-dimethylcyclopentadienyl)(3xe2x80x2,5xe2x80x2-dimethylcyclopentadienyl)zirconium dichloride, rac-dimethylsilylene(2,4-dimethylcyclopentadienyl)(3xe2x80x2,5xe2x80x2-dimethylcyclopentadienyl)zirconium dimethyl, rac-dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2xe2x80x2,4xe2x80x2,5xe2x80x2-trimethylcyclopentadienyl)zirconium dichloride, rac-dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2xe2x80x2,4xe2x80x2,5xe2x80x2,5xe2x80x2-trimethylcyclopentadienyl)zirconium dimethyl, rac-dimethylsilylenebis(2-methyl-indenyl)zirconium dichloride, rac-diphenylsilylenebis(2-methyl-indenyl)zirconium dichloride, rac-dimethylsilylenebis(2-methyl-indenyl)zirconium dimethyl, rac-diphenylsilylenebis(2-methyl-indenyl)zirconium dimethyl, rac-dimethylsilylenebis(2-methyl-4,5,6,7-tetrahydroindenyl)zirconium dichloride, rac-diphenylsilylenebis(2-methyl-4,5,6,7-tetrahydroindenyl)zirconium dichloride, rac-dimethylsilylenebis(2-methyl-4,5,6,7-tetrahydroindenyl)zirconium dimethyl, rac-diphenylsilylenebis(2-methyl-4,5,6,7-tetrahydroindenyl)zirconium dimethyl, rac-dimethylsilylenebis(2,4-dimethyl-indenyl)zirconium dichloride, rac-diphenylsilylenebis(2,4-dimethyl-indenyl)zirconium dichloride, rac-dimethylsilylenebis(2,4-dimethyl-indenyl)zirconium dimethyl, rac-diphenylsilylenebis(2,4-dimethyl-indenyl)zirconium dimethyl, rac-dimethylsilylenebis(2-methyl-4-isopropylindenyl)zirconium dichloride, rac-diphenylsilylenebis(2-methyl-4-isopropylindenyl)zirconium dichloride, rac-dimethylsilylenebis(2-methyl-4-isopropylindenyl)zirconium dimethyl, rac-diphenylsilylenebis(2-methyl-4-isopropylindenyl)zirconium dimethyl, rac-dimethylsilylenebis(2-methyl-4,6-diisopropylindenyl)zirconium dichloride, rac-diphenylsilylenebis(2-methyl-4,6-diisopropylindenyl)zirconium dichloride, rac-dimethylsilylenebis(2-methyl-4,6-diisopropylindenyl)zirconium dimethyl, rac-diphenylsilylenebis(2-methyl-4,6-diisopropylindenyl)zirconium dimethyl, rac-dimethylsilylenebis(2-methyl-4-t-butylindenyl)zirconium dichloride, rac-diphenylsilylenebis(2-methyl-4-t-butylindenyl)zirconium dichloride, rac-dimethylsilylenebis(2-methyl-4-t-butylindenyl)zirconium dimethyl, rac-diphenylsilylenebis(2-methyl-4-t-butylindenyl)zirconium dimethyl, rac-dimethylsilylenebis(2-methyl-4-phenylindenyl)zirconium dichloride, rac-diphenylsilylenebis(2-methyl-4-phenylindenyl)zirconium dichloride, rac-dimethylsilylenebis(2-methyl-4-phenylindenyl)zirconium dimethyl, rac-diphenylsilylenebis(2-methyl-4-phenylindenyl)zirconium dimethyl, rac-dimethylsilylenebis(2-methyl-4-naphthylindenyl)zirconium dichloride, rac-diphenylsilylenebis(2-methyl-4-naphthylindenyl)zirconium dichloride, rac-dimethylsilylenebis(2-methyl-4-naphthylindenyl)zirconium dimethyl, rac-diphenylsilylenebis(2-methyl-4-naphthylindenyl)zirconium dimethyl, rac-dimethylsilylenebis(2-methyl-benzindenyl)zirconium dichloride, rac-diphenylsilylenebis(2-methyl-benzindenyl)zirconium dichloride, rac-dimethylsilylenebis(2-methyl-benzindenyl)zirconium dimethyl, rac-diphenylsilylenebis(2-methyl-benzindenyl)zirconium dimethyl and the like.
Compounds obtained by replacing the zirconium of the above compounds by hafnium may be advantageously used. The above metallocene compounds may be used in combination.
Out of the above components (II), aluminum compounds represented by the following formulas (2) or (3) are preferred as the aluminoxane compound. 
In the above formulas (2) and (3), R is an alkyl group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. Examples of the alkyl group include methyl group, ethyl group, propyl group, butyl group and isobutyl group, out of which methyl group is preferred. Part of R""s may be an alkyl group having 2 to 6 carbon atoms. m is an integer of 4 to 100, preferably 6 to 80, particularly preferably 10 to 60.
To produce the above aluminoxane compound, various known methods may be employed. They include one in which a trialkylaluminum is directly reacted with water in a hydrocarbon solvent and one in which a trialkylaluminum is reacted with water adsorbed in a hydrocarbon solvent using copper sulfate hydrate having crystallization water, aluminum sulfate hydrate, hydrated silica gel or the like.
Out of the above components (II), known non-coordination ionized compounds other than the above aluminoxane compounds are used as the non-coordination ionized compound. Ionized compounds containing a boron atom are particularly preferred.
Out of the ionized compounds containing a boron atom, Lewis acid containing a boron atom and ionic compounds containing a boron atom are preferred. The Lewis acid containing a boron atom is a compound represented by the following formula (4).
BR3 xe2x80x83xe2x80x83(4)
In the above formula, R is a phenyl group having a substituent such as a fluorine atom, methyl group or trifluoromethyl group, or fluorine atom.
Illustrative examples of the compound represented by the above formula (4) include trifluoroborane, triphenylborane, tris(4-fluorophenyl)borane, tris(3,5-diflurophenyl)borane, tris(4-fluoromethylphenyl)borane, tris(pentafluorophenyl)borane, tris(p-tolyl)borane, tris(o-tolyl)borane, tris(3,5-dimethylphenyl)borane and the like. Out of these, tris(pentafluoro)borane is preferred.
The ionic compound containing boron is a trialkyl-substituted ammonium salt, N,N-dialkylanilinium salt, dialkylammonium salt, triaryl phosphonium salt or the like. Specific examples of the trialkyl-substituted ammonium salt include triethylammonium tetra(phenyl)boron, tripropylammoniumtetra(phenyl)boron, tri(n-butyl)ammonium tetra(phenyl)boron, trimethylammonium (p-tolyl)boron, trimethylammonium tetra(o-tolyl)boron, tributylammonium tetra(pentafluorophenyl)boron, tripropylammonium tetra(o,p-dimethylphenyl)boron, tributylammonium tetra(m,m-dimethylphenyl)boron, tributylammonium tetra(p-trifluoromethylphenyl)boron, tri(n-butyl)ammonium tetra(o-tolyl)boron and the like. Examples of the N,N-dialkylanilinium salt include N,N-dimethylanilinium tetra(phenyl)boron, N,N-diethylanilinium tetra(phenyl)boron, N,N-2,4,6-pentamethylanilinium tetra(phenyl)boron and the like. Examples of the dialkylammonium salt include di(1-propyl)ammonium tetra(pentafluorophenyl)boron, dicyclohexylammonium tetra(phenyl)boron and the like. Examples of the triarylphosphonium salt include triphenylphosphonium tetra(phenyl)boron, tri(methylphenyl)phosphonium tetra(phenyl)boron, tri(dimethylphenyl)phosphonium tetra(phenyl)boron and the like.
Out of the Lewis acids containing a boron atom and the ionic compounds containing a boron atom listed above, triphenylcarbonium tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate and ferrocenium tetra(pentafluorophenyl)borate are preferred. Triphenylcarbonium tetrakis(pentafluorophenyl)borate and N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate are more preferred.
The components (I) and (II) may be used in any amounts. When an aluminoxane compound is used as the component (II), the amount of the component (II) (the molar amount of an A1 atom in the component (II)) is preferably 0.1 to 100,000 mols, more preferably 1 to 50,000 mols, particularly preferably 10 to 30,000 mols based on 1 mol of a transition metal atom contained in the component (I). When a non-coordination ionized compound is used as the component (II), the amount of the component (II) (the molar amount of the 3B group atom in the component (II)) is preferably 0.01 to 10,000 mols, more preferably 0.1 to 5,000 mols, particularly preferably 1 to 3,000 mols based on 1 mol of a transition metal contained in the component (I).
An organic aluminum compound (to be referred to as xe2x80x9ccomponent (III)xe2x80x9d hereinafter) may be used as required in the method of producing the polypropylene component (a) and the propylene-ethylene copolymer component (b) stepwise in the presence of a catalyst which comprises the component (I) and the component (II). The component (III) is preferably a compound represented by the following formula (5):
AlRmX3-mxe2x80x83xe2x80x83(5)
wherein R is an alkyl group having 1 to 10 carbon atoms, hydrocarbon group such as an aryl group or alkoxy group, X is a halogen atom, and m is an integer of 1 to 3 indicating the valence of A1.
Illustrative examples of the compound represented by the above formula (5) include trialkylaluminums such as trimethylaluminum, triethylaluminum, tri-n-propylaluminum, triisopropylaluminum, tri-n-butylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum and tri-n-decylaluminum; dialkylaluminum monohalides such as diethylaluminum monochloride, diethylaluminum monobromide and diethylaluminum monofluoride; alkylaluminum halides such as methylaluminum sesquichloride, ethylaluminum sesquichloride and ethylaluminum dichloride; and alkoxyaluminums such as diethylaluminum monoethoxide and ethylaluminum diethoxide. Out of these, trialkylaluminums such as trimethylaluminum, triethylaluminum and triisobutylaluminum are preferred.
The amount of the component (III) is preferably 1 to 50,000 mols, more preferably 5 to 10,000 mols, particularly preferably 10 to 5,000 mols based on 1 mol of a transition metal atom contained in the component (I).
The component (I) and/or the component (II) may be carried on a particulate carrier (to be referred to as xe2x80x9ccomponent (IV)xe2x80x9d hereinafter). When the above catalyst component(s) is(are) carried on the carrier, the particle properties of the obtained polymer are improved, thereby making it possible to prevent the adhesion of polymer scales to a reactor and greatly improve process applicability to the production of a resin.
The particulate carrier is what has a function as a carrier, particularly preferably an inorganic oxide.
Illustrative examples of the inorganic oxide include SiO2, Al2O3, MgO, ZrO2, TiO2, B2O3, CaO, ZnO, BaO, ThO2, and mixtures thereof such as SiO2xe2x80x94Al2O3, SiO2xe2x80x94MgO, SiO2xe2x80x94TiO2, SiO2xe2x80x94V2O5, SiO2xe2x80x94Cr2O3 and SiO2xe2x80x94TiO2xe2x80x94MgO. Out of these, carriers containing at least one component selected from the group consisting of SiO2 and Al2O3 as the main ingredient are preferred.
The carrier preferably used in the present invention, whose properties differ according to its type and production method, has a particle diameter of 10 to 300 xcexcm, preferably 20 to 200 xcexcm, a specific surface area of 50 to 1,000 m3/g, preferably 100 to 700 m3/g and a pore volume of 0.3 to 3.0 cm3/g, preferably 0.5 to 2.5 cm3/g.
The inorganic particulate carrier is baked at preferably 150 to 1,000xc2x0 C., more preferably 200 to 800xc2x0 C.
The particle diameter of the carrier is preferably 0.1 to 500 xcexcm, more preferably 1 to 200 xcexcm, particularly preferably 10 to 100 xcexcm. When the particle diameter is too small, a fine powder polymer is formed and when the particle diameter is too large, coarse particles are formed, thereby making it difficult to handle powders.
The pore volume of the carrier is preferably 0.1 to 5 cm3/g, more preferably 0.3 to 3 cm3/g. The pore volume can be measured by a BET method or mercury intrusion porosity method.
The amount of the metallocene compound (I) based on 1 g of the above particulate carrier (IV) is 0.005 to 1 mmol, preferably 0.05 to 0.5mmol in terms of transition metal atoms. When an aluminoxane compound is used as the component (II), the amount of the aluminoxane compound is preferably 1 to 200 mols, more preferably 15 to 150 mols in terms of the molar amount of an A1 atom based on 1 mol of a transition metal atom contained in the component (I).
When a non-coordination ionized compound is used as the component (II), the amount of the non-coordination ionized compound is preferably 0.1 to 20 mols, more preferably 1 to 15 mols in terms of the molar amount of the group XIII atom contained in the non-coordination ionized compound based on 1 mol of a transition metal atom in the component (I).
To obtain a polymer having more excellent particle properties, the following methods may be employed. That is, an olefin is prepolymerized in the presence of the above components (I), (II) and (IV) and the component (III) as required. The amount of the component (III) to be prepolymerized is preferably 1 to 50,000 mols, more preferably 5 to 10,000 mols, particularly preferably 10 to 5,000 mols based on 1 mol of a transition metal atom contained in the component (I). The above components used for prepolymerization may be added sequentially or simultaneously in the form of a mixture. Preferably, the components (I) and (II) are contacted to the catalyst component (IV) in advance. More preferably, the component (II) is carried on the catalyst component (IV) and then the component (I) is carried on the catalyst component (IV). This method is effective in obtaining a random copolymer having a more excellent bulk specific gravity.
Examples of the olefin prepared for the preparation of a prepolymerization catalyst component include xcex1-olefins such as ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-heptene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 3-ethyl-1-hexene, 4-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene; and cyclic olefins such as cyclopentene, cycloheptene, norbornene, 5-methyl-2-norbornene, tetracyclododecene and 2-methyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene. In addition to these, styrene, dimethylstyrenes, allylnorbornene, allylbenzene, allylnaphthalene, allyltoluenes, vinylcyclopentane, vinylcyclohexane, vinylcycloheptane and dienes may also be used. Out of these, ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-heptene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 3-ethyl-1-hexene, 4-ethyl-1-hexene, 1-octene, 1-decene, cyclopentene and vinylcyclohexane are preferred, and ethylene, propylene, 1-butene, 1-heptene, 3-methyl-1-butene, 1-hexene and 4-methyl-1-pentene are particularly preferred.
Prepolymerization is preferably the homopolymerization of 95 mol % or more of an olefin.
The amount of an olefin to be prepolymerized firstly in the present invention is preferably 0.1 to 1,000 g, more preferably 1 to 50 g based on 1 g of a catalyst formed from the catalyst components (I), (II) and (IV).
Particularly preferably, prepolymerization is carried out stepwise in such a manner that propylene is prepolymerized in the presence of the components (I), (II) and (IV) and the component (III) as required to obtain a first prepolymerization catalyst and then 1-butene is prepolymerized in the presence of the first prepolymerization catalyst and the above component (III).
The amount of the component (III) used for the prepolymerization is preferably 1 to 50,000 mols, more preferably 5 to 10,000 mols, particularly preferably 10 to 5,000 mols based on 1 mol of a transition metal atom contained in the component (I). After the first prepolymerization catalyst is obtained by the prepolymerization of propylene, unreacted propylene and the component (III) used as required are desirably removed by washing and then used for the subsequent prepolymerization.
Substantial homopolymerizations of 95 mol % or more, preferably 98 mol % or more each of propylene and 1-butene are carried out in the above prepolymerization stages.
The amount of propylene first prepolymerized is preferably 0.1 to 1,000 g, more preferably 1 to 10 g based on 1 g of a catalyst formed from the catalyst components (I), (II) and (IV). The amount of 1-butene prepolymerized subsequently is preferably 0.1 to 1,000 g, more preferably 1 to 500 g based on 1 g of a catalyst formed from the components (I), (II) and (III). The weight ratio of propylene to 1-butene is preferably 0.001 to 100, more preferably 0.005 to 10.
Slurry polymerization is preferably applied in prepolymerization. The solvent used for the slurry polymerization is a saturated aliphatic hydrocarbon such as hexane, heptane, cyclohexane, benzene or toluene, aromatic hydrocarbon or mixture thereof. The prepolymerization temperature is preferably xe2x88x9220 to 100xc2x0 C., more preferably 0 to 60xc2x0 C. The prepolymerization stages may be carried out at different temperatures. The prepolymerization time is suitably determined according to the prepolymerization temperature and the amount of prepolymerization. The prepolymerization pressure is, for example, atmospheric pressure to 5 kg/cm2 in the case of slurry polymerization.
Prepolymerization of each stage may be carried out in either batch, semi-batch or continuous system.
After the end of prepolymerization, the obtained polymer is preferably washed with a saturated aliphatic hydrocarbon such as hexane, heptane, cyclohexane, benzene or toluene, aromatic hydrocarbon or mixed solvent thereof. The number of times of washing is preferably 5 to 6.
The modifier (A1) is produced by polymerizing a polypropylene component and a propylene-ethylene copolymer component stepwise in the presence of the above catalyst components. As for polymerization order, the polypropylene component (a) is preferably formed in the first stage and the propylene-ethylene copolymer component (b) in the second stage. Thereby, a polymer having excellent particle properties can be produced.
The polymerization of the polypropylene component (a) is carried out by supplying propylene alone or a mixture of propylene and other xcex1-olefin including ethylene. The temperature for the polymerization of propylene is preferably 0 to 100xc2x0 C., more preferably 20 to 80xc2x0 C.
Hydrogen may be existent as a molecular weight modifier during the polymerization. Polymerization may be slurry polymerization using a monomer for use in polymerization as a solvent, vapor-phase polymerization or solution polymerization. Slurry polymerization using propylene itself as a solvent is preferred when process simplicity, reaction rate and the particle properties of the formed copolymer are taken into consideration.
Polymerization system may be either batch, semi-batch or continuous. Further, polymerization may be carried out in two or more stages under different conditions such as hydrogen concentration and polymerization temperature.
Thereafter, the random copolymerization of propylene and ethylene is carried out. The random copolymer component (b) of propylene and ethylene can be obtained by supplying ethylene gas continuously even after the polymerization of propylene in the case of slurry polymerization using propylene itself as a solvent or supplying mixed gas of propylene and ethylene in the case of vapor-phase polymerization.
The random copolymerization of propylene and ethylene is preferably carried out in a single stage after the polymerization of propylene but may be carried out in multiple stages by changing the concentration of ethylene. The temperature for the random copolymerization of propylene and ethylene is preferably 0 to 100xc2x0 C., more preferably 20 to 80xc2x0 C. Hydrogen may be used as a molecular weight modifier as required. Polymerization may be carried out by changing the concentration of hydrogen stepwise or continuously.
The random copolymerization system of propylene and ethylene may be either batch, semi-batch or continuous. Polymerization may be carried out in multiple stages. Polymerization may be slurry polymerization, vapor-phase polymerization or solution polymerization.
After the end of the polymerization, the monomers are evaporated from a polymerization system to obtain the propylene-based resin (modifier (A1)) of the present invention. This propylene-based resin may be subjected to conventional washing with a hydrocarbon having 7 or less carbon atoms or countercurrent washing.
Production of Crystalline Polyolefin Resin Composition
The method of producing the crystalline polyolefin resin composition of the present invention by mixing the above modifier (A1) with the crystalline polyolefin resin is not particularly limited. For instance, a powder blending method using a tumbler, Henschel mixer or the like, or pellet blending method may be used.
The crystalline polyolefin resin composition of the present invention may also be produced by forming the effective components of the modifier (A1) and the crystalline polyolefin in the same polymerization system and mixing the both components formed in the polymerization system. For example, several different polymerization catalyst components capable of forming polypropylene resins which differ from each other in isotacticity are mixed together to polymerize propylene. A method of polymerizing propylene by mixing a solid titanium catalyst component, organic aluminum compound and two or more electron donors which give polypropylene resins different from each other in isotacticity is particularly preferably employed. In this method, known electron donors which are generally used in the polymerization of propylene may be used without restriction. When an organic silicon compound represented by the following formula (V) or (VI) is used out of these, a composition containing a component having an elution temperature of 36 to 104xc2x0 C. and a molecular weight of 100,000 to 1,000,000 measured by TREF/SEC in amount of 4 to 20 wt % is obtained with ease. 
wherein R1, R2 and R3 are the same or different hydrocarbon groups, and n is 0 or 1.
Known compounds which are used for the polymerization of propylene may be used as the above solid titanium catalyst component. Solid titanium catalyst components containing titanium, magnesium or halogen and having high catalytic activity are particularly preferred. The catalyst components are titanium halides, particularly titanium tetrachloride carried on various magnesium compounds, particularly magnesium chloride.
Known compounds which are used for the polymerization of propylene may be used as the organic aluminum compound, as exemplified by trialkylaluminums such as trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, tri-isobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum and tri-n-decylaluminum; diethylaluminum monohalides such as diethylaluminum monochloride; and alkylaluminum halides such as methylaluminum dichloride and ethylaluminum dichloride. Alkoxyaluminums such as monoethoxy diethylaluminum and diethoxy monoethylaluminum may also be used. Out of these, triethylaluminum is the most preferred. As for the amount of the organic aluminum compound, the molar ratio of aluminum atoms to titanium atoms contained in the solid titanium catalyst component is preferably 10 to 1,000, more preferably 50 to 500.
In the organic silicon compounds represented by the above formulas (V) and (VI), the hydrocarbon groups represented by R1, R2 and R3 may be chain, branched or cyclic aliphatic hydrocarbon groups and aromatic hydrocarbon groups. The number of carbon atoms of the hydrocarbon groups is not particularly limited. The hydrocarbon groups preferably used in the present invention include alkyl groups having 1 to 6 carbon atoms such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, s-butyl group, t-butyl group, pentyl group and hexyl group; alkenyl groups having 2 to 6 carbon atoms such as vinyl group, propenyl group and allyl group; alkinyl groups having 2 to 6 carbon atoms such as ethynyl group and propynyl group; cycloalkyl groups having 5 to 7 carbon atoms such as cyclopentyl group, cyclohexyl group and cycloheptyl group; and aryl groups having 6 to 12 carbon atoms such as phenyl group, tolyl group, xylyl group and naphthyl group. Out of these, R3 is preferably a linear alkyl group, alkenyl group or aryl group. n is 0 or 1.
Illustrative examples of the organic silicon compound represented by the formula (V) preferably used in the present invention include dimethyldimethoxysilane, diethyldimethoxysilane, dipropyldimethoxysilane, divinyldimethoxysilane, diallyldimethoxysilane, di-1-propenyldimethoxysilane, diethyldimethoxysilane, diphenyldimethoxysilane, methylphenyldimethoxysilane, cyclohexylmethyldimethoxysilane, tertiary-butylethyldimethoxysilane, ethylmethyldimethoxysilane, propylmethyldimethoxysilane, cyclohexyltrimethoxysilane, diisopropyldimethoxysilane, dicyclopentyldimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, allyltrimethoxysilane and the like.
Illustrative examples of the organic silicon compound represented by the above formula (VI) include tetraethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, vinyltriethoxysilane, butyltriethoxysilane, pentyltriethoxysilane, isopropyltriethoxysilane, 1-propenyltriethoxysilane, isopropenyltriethoxysilane, ethynyltriethoxysilane, octyltriethoxysilane, dodecyltriethoxysilane, phenyltriethoxysilane, allyltriethoxysilane and the like.
As for the amount of the organic silicon compound represented by the above formula (V) or (VI), the molar ratio of silicon atoms to titanium atoms contained in the solid titanium catalyst component is preferably 0.1 to 500, more preferably 1 to 100. The molar ratio (V/VI) of the two different organic silicon compounds is preferably 1:5 to 1:25, more preferably 1:10 to 1:20. When the molar ratio of the organic silicon compounds (V) and (VI) is smaller than 1:5, the elution peak width measured by TREF of the obtained polypropylene resin becomes narrow, that is, the amount of a component having an elution temperature of 36 to 104xc2x0 C. decreases, thereby reducing stretchability at the time of film formation, increasing a metal load and causing the breakage of a film by stretching very often.
The addition order of the above components is not particularly limited. The organic silicon compounds represented by the above formulas (V) and (VI) may be supplied at the same time or separately. They may be contacted to or mixed with the organic aluminum compound and then supplied.
Other preferred polymerization conditions are as follows. The polymerization temperature is preferably 20 to 200xc2x0 C., more preferably 50 to 150xc2x0 C. Hydrogen may be existent in polymerization as a molecular weight modifier. Polymerization may be slurry polymerization, solvent-free polymerization or vapor-phase polymerization and may be carried out in batch, semi-batch or continuous system. Polymerization may be carried out in two stages under different conditions. Before the polymerization of propylene, the prepolymerization of propylene or other monomer may be carried out. The above polymerization may be carried out in multiple stages.
In the present invention, the polypropylene resin composition obtained by the above method may be used alone or blended with other polypropylene resin. Polypropylene resin compositions obtained by the above method may be blended together as a matter of course.
In the present invention, a polyolefin resin composition containing a component having an elution temperature of 36 to 104xc2x0 C. and a molecular weight of 100,000 to 1,000,000 measured by TREF/SEC in an amount of 4 to 20 wt % can be obtained directly from the polyolefin resin composition obtained as described above or by selecting an appropriate polyolefin resin composition obtained as described above. Alternatively, the crystalline polyolefin resin composition of the present invention having desired composition can be obtained by mixing the modifier (A1) or crystalline polyolefin resin with the above resin composition.
The crystalline polyolefin resin composition of the present invention which comprises a modifier (A1) and a modifier (A2) containing a component having an elution temperature of more than 116xc2x0 C. and a molecular weight of 10,000 to 100,000 measured by TREF/SEC in an amount of 20 to 100 wt % can be obtained in the same manner as described above. Alternatively, the crystalline polyolefin resin composition of the present invention may be obtained by mixing the modifier (A1) and the modifier (A2) which contains a component having an elution temperature of more than 116xc2x0 C. and a molecular weight of 10,000 to 100,000 measured by TREF/SEC in an amount of 20 to 100 wt % with the crystalline polyolefin resin.
Modifier (A2)
The above modifier (A2) is a highly crystalline polypropylene resin. The melt flow rate of the modifier (A2) is preferably 5 to 100 g/10 min, more preferably in the range of 30 to 80 g/10 min in consideration of moldability into a film. The weight average molecular weight (Mw) of the modifier (A2) is preferably in the range of 50,000 to 800,000, more preferably 100,000 to 300,000.
The molecular weight distribution (Mw/Mn) of the modifier (A2) is preferably 1.5 to 40, more preferably 2 to 10 in consideration of film forming ease and the improvement of workability caused by an increase in melt tension.
The melting point of the above modifier (A2) is preferably 150xc2x0 C. or more, more preferably 155 to 170xc2x0 C.
The peak top temperature of an elution curve measured by TREF of the modifier (A2) is preferably 110xc2x0 C. or more, more preferably 115 to 130xc2x0 C. in consideration of the rigidity and heat resistance of the formed oriented film.
The component having an elution temperature of 0xc2x0 C. or less measured by TREF/SEC of the modifier (A2) is preferably contained in an amount of 5 wt % or less, more preferably 3 wt % or less in consideration of the surface properties such as anti-blocking properties, scratch resistance and slipperiness of the formed polyolefin film.
When the modifier (A2) is a propylene homopolymer or propylene-xcex1-olefin copolymer and contains an xcex1-olefin other than propylene in an amount of less than 1 mol %, the fraction of isotactic pentad sequence measured by 13C-NMR and indicating the crystallizability of the modifier is preferably 0.80 to 1, more preferably 0.93 to 0.99.
Alternatively, a modifier (to be referred to as xe2x80x9cmodifier (A1/A2)xe2x80x9d) may be obtained by mixing the modifier (A1) and the modifier (A2) in a ratio of 20/80 or 80/20 and mixed with the crystalline resin.
The weight ratio (A2/A1) of the effective component of the modifier (A1) to the effective component of the modifier (A2) to be mixed with the crystalline polyolefin resin is preferably in the range of 0.5 to 2, more preferably 0.8 to 1.5. Within the above range, the effect of improving stretchability at the time of film formation, that is, the expansion of the width of film processable temperature, a reduction in mechanical load, a reduction in film breakage and the improvement of thickness accuracy for stretching can be made possible.
Other Components
The polyolefin resin composition of the present invention may contain additives such as an antioxidant, chlorine trapping agent, heat stabilizer, antistatic agent, anti-fogging agent, ultraviolet light absorber, lubricant, nucleating agent, anti-blocking agent, pigment, other resin and filler as required in limits that do not prevent the effect of the present invention.
Molding of Polyolefin Resin Composition
The polyolefin resin composition of the present invention may be used in the production of all kinds of moldings and exhibits excellent extrudability and stretchability. Particularly, it shows a marked effect when it is stretched to obtain an oriented film.
The polyolefin oriented film of the present invention may be either a biaxially oriented or uniaxially oriented film. The thickness of the oriented film is preferably 3 to 150 xcexcm in the case of a biaxially oriented film and 10 to 254 xcexcm in the case of a uniaxially oriented film. The draw ratio is 4 to 10 times in a uniaxial direction and further 4 to 15 times in a direction perpendicular to the above uniaxial direction in the case of biaxial orientation.
One side or both sides of the polyolefin oriented film of the present invention may be surface treated by corona discharge or the like as required. Further, a layer of other resin having a lower melting point than the polyolefin resin used in the present invention may be formed on one side or both sides of the polyolefin oriented film to provide such a function as heat sealability. The method of forming the other resin layer on the polyolefin oriented film is not particularly limited but it is preferably coextrusion or lamination.
To produce the polyolefin oriented film of the present invention, known methods may be employed. For example, when an oriented film is formed by sequential biaxial orientation using a tenter, the above polypropylene resin composition is formed into a sheet or film by a T-die method or inflation method, the sheet or film is supplied to avertical stretching machine to be stretched to 3 to 10 times in a longitudinal direction at a heating roll temperature of 120 to 170xc2x0 C. and then stretched to 4 to 15 times in a transverse direction at a tenter temperature of 130 to 180xc2x0 C. using a tenter. The above molding conditions are not particularly limited. However, to obtain an oriented film having excellent thickness accuracy and fusing sealability, the sheet or film is preferably stretched to 3 to 5 times in a longitudinal direction at 145 to 170xc2x0 C. and to 4 to 12 times in a transverse direction at 155 to 180xc2x0 C. Further, it is heat set at 80 to 180xc2x0 C. while it is relaxed by 0 to 25% in a transverse direction as required. As a matter of course, it may be stretched again after this and multi-stage stretching and rolling may be combined for stretching in a longitudinal direction. An oriented film may be obtained by stretching in only a uniaxial direction.
The polyolefin resin composition of the present invention is characterized in that it has a wider range of film processable temperature than conventionally known polyolefin resins, the mechanical load at the time of stretching is small, the thickness accuracy of the formed film is high, stretchability is satisfactory and film breakage by stretching hardly occurs. Therefore, the polyolefin resin composition of the present invention is a polyolefin resin composition which allows for stable and continuous operation and is suitable for the production of an oriented film. Further, the formed oriented film has excellent heat resistance such as thermal shrinkage. These effects show that the polyolefin resin composition of the present invention is excellent as a polyolefin resin composition for an oriented film and of great industrial value.